MaximumSubarray.java

package leetcode;

/**
 * Project Name : Leetcode
 * Package Name : leetcode
 * File Name : MaximumSubarray
 * Creator : Leo
 * Description : TODO
 */
public class MaximumSubarray {
    /**
     * 53. Maximum Subarray
     *
     * Find the contiguous subarray within an array (containing at least one number) which has the largest sum.

     For example, given the array [-2,1,-3,4,-1,2,1,-5,4],
     the contiguous subarray [4,-1,2,1] has the largest sum = 6.

     * @param nums
     * @return
     */

    // time : O(n) space : O(n);
    public int maxSubArray(int[] nums) {
        int[] dp = new int[nums.length];
        dp[0] = nums[0];
        int res = nums[0];
        for (int i = 1; i < nums.length; i++) {
            dp[i] = nums[i] + (dp[i - 1] < 0 ? 0 : dp[i - 1]);
            res = Math.max(res, dp[i]);
        }
        return res;
    }

    // time : O(n) space : O(1);
    public int maxSubArray2(int[] nums) {
        int res = nums[0];
        int sum = nums[0];
        for (int i = 1; i < nums.length; i++) {
            sum = Math.max(nums[i], sum + nums[i]);
            res = Math.max(res, sum);
        }
        return res;
    }
}